CVE-2023-6449: Contact Form 7 Auth Bypass Vulnerability

CVE-2023-6449 Overview

CVE-2023-6449 affects the Contact Form 7 plugin for WordPress, one of the most widely deployed form plugins on the platform. The vulnerability stems from insufficient file type validation in the validate function and incomplete blocklisting in the wpcf7_antiscript_file_name function. Authenticated attackers with editor-level capabilities or above can upload arbitrary files to the affected site's server. The flaw is classified under [CWE-434] Unrestricted Upload of File with Dangerous Type. The vulnerability impacts all versions of Contact Form 7 up to and including 5.8.3, and is resolved in version 5.8.4.

Critical Impact

Authenticated editors can upload arbitrary files to the WordPress server. While default .htaccess restrictions and immediate file deletion limit direct remote code execution, the flaw can be chained with local file inclusion or other plugin behaviors to achieve code execution.

Affected Products

• Rocklobster Contact Form 7 plugin for WordPress, all versions up to and including 5.8.3
• WordPress sites running editor-level or higher accounts with the vulnerable plugin active
• Sites running additional plugins that may preserve uploaded files beyond the default deletion window

Discovery Timeline

• 2023-11-30 - Rocklobster releases Contact Form 7 version 5.8.4 with the security fix
• 2023-12-01 - CVE-2023-6449 published to NVD
• 2026-04-08 - Last updated in NVD database

Technical Details for CVE-2023-6449

Vulnerability Analysis

The vulnerability resides in two interrelated components of the Contact Form 7 file upload flow. The validate function does not enforce strict file type checks before accepting uploads through form submissions. The complementary wpcf7_antiscript_file_name function relies on a blocklist that fails to cover all dangerous file extensions and naming patterns.

Because the blocklist is incomplete, attackers can craft filenames that pass the sanitization routine while still carrying executable content or scripting payloads. Authenticated users with editor-level capabilities or higher can leverage this to write arbitrary files into the upload directory on the server.

Direct remote code execution is typically prevented by the default .htaccess configuration shipped with the plugin, which blocks execution within the upload path. Contact Form 7 also deletes uploaded files immediately after processing the form submission. However, both protections can be undermined by environment-specific factors.

Root Cause

The root cause is a deny-list approach to filename sanitization in wpcf7_antiscript_file_name, combined with weak MIME and extension enforcement in validate. Deny-list filtering is a known anti-pattern for upload security since attackers can always identify extensions, double extensions, or case variants not covered by the list. The fix in version 5.8.4 extends the filtering logic to cover additional dangerous extensions and tightens validation flow.

Attack Vector

Exploitation requires authenticated access with editor-level capabilities or above, which raises the bar but does not eliminate risk on multi-author sites. The attacker submits a crafted form with a file attachment whose name and extension evade the blocklist. The plugin writes the file to the uploads directory under the WordPress installation. If another installed plugin preserves the file beyond Contact Form 7's deletion routine, or if the web server is not honoring the bundled .htaccess, the file remains accessible. Chaining this primitive with a local file inclusion vulnerability in another component converts the upload into remote code execution.

No public proof-of-concept exploit code has been published for this issue. Technical details are documented in the Wordfence Vulnerability Report and the GitHub Change Comparison.

Detection Methods for CVE-2023-6449

Indicators of Compromise

• Unexpected files in the wp-content/uploads/wpcf7_uploads/ directory, especially files with executable extensions or double extensions such as .phtml, .phar, .pht, or .php.jpg
• Form submission requests to /wp-json/contact-form-7/v1/contact-forms/*/feedback containing multipart attachments with suspicious filenames
• Editor or administrator accounts submitting forms with file attachments outside of normal usage patterns
• New or modified PHP files in WordPress directories shortly after Contact Form 7 submissions

Detection Strategies

• Audit installed Contact Form 7 versions across all WordPress sites and flag any instance at or below 5.8.3
• Monitor web server access logs for POST requests to Contact Form 7 endpoints followed by GET requests to uploaded file paths
• Inspect file integrity monitoring alerts for new files written under WordPress upload directories with non-standard extensions
• Correlate authenticated session activity from editor-level accounts with file upload events to identify abuse of legitimate credentials

Monitoring Recommendations

• Enable WordPress audit logging to capture form submissions, file uploads, and user role activity
• Forward web server, PHP error, and WordPress audit logs to a centralized analytics platform for cross-source correlation
• Establish alerting on creation of executable file types within wp-content/uploads/ regardless of source plugin
• Track installations of plugins known to interact with Contact Form 7 uploads, since they may extend file lifetime beyond the default deletion window

How to Mitigate CVE-2023-6449

Immediate Actions Required

• Update Contact Form 7 to version 5.8.4 or later on every WordPress instance using the plugin
• Review editor, author, and administrator accounts and remove unused or excessive privileges
• Inspect the wpcf7_uploads directory and broader wp-content/uploads/ tree for unexpected files and remove any artifacts
• Audit other installed plugins for behaviors that may copy, move, or retain Contact Form 7 attachments

Patch Information

Rocklobster addressed the issue in Contact Form 7 5.8.4, released on 2023-11-30. The patch strengthens the wpcf7_antiscript_file_name filtering and revises the validate function. Patch details are available in the Contact Form 7 Release Note, the GitHub Change Comparison, and the WordPress Trac Changeset.

Workarounds

• Disable file attachment fields in Contact Form 7 forms until the plugin can be updated
• Confirm the .htaccess file in wp-content/uploads/wpcf7_uploads/ is present and that the web server honors AllowOverride directives
• Enforce strict server-side execution restrictions on the uploads directory at the web server configuration level, independent of .htaccess
• Restrict editor-level and above accounts using multi-factor authentication and strong password policies to limit prerequisite access

# Nginx configuration to deny execution within WordPress upload paths
location ~* /wp-content/uploads/.*\.(php|phtml|phar|pht|php3|php4|php5|php7|php8)$ {
    deny all;
    return 403;
}